Ferromagnetic materials have the property of becoming magnetic, i.e. of being magnetised, when placed in a magnetic field, and of keeping part of this magnetism when the field is removed.
Ferromagnetic materials are composed of metal elements such as iron (mainly), nickel and cobalt that allow strong magnetisation to be achieved.
The interior of ferromagnetic materials is split into small domains in which all the atoms have parallel magnetisation. These domains tend to align in the direction of an external magnetic field, making the material strongly magnetic.
Ferromagnetic substances are used for their magnetic properties because, not only can they be strongly magnetised, they can remain so through the magnetic hysteresis phenomenon.